The invention disclosed herein pertains to apparatus for lubricating a journal bearing with a disk mounted concentrically to a shaft wherein the disk rotates through oil in a sump and transports the oil to a level above the bearing where the oil is scraped from the disk and directed into the bearing for lubricating it.
Experience has shown that in conventional disk lubricated journal bearings, the disk transports sufficient oil to lubricate a large journal bearing at rotational speeds of 30 rpm or even less. As rotational speed of the shaft increases, even more oil is transported and the journal is assuredly well-lubricated. But, in some designs, when the rotational speed of the shaft increases substantially, such as to over 130 rpm, the amount of oil delivered to the bearing actually decreases because so much more oil is centrifuged from the disk before the oil carried by the disk can get to the scraper where it is to be diverted to the bearing. At high shaft speeds, the oil is spun from the disk against the interior surface of the bearing housing. In machines, such as two pole alternators which run at 3600 rpm, disk-lubricated bearings are not ordinarily used. Instead, the usual practice is to provide a forced feed lubrication system in which a pump forces oil into the bearing, and the oil is cooled before it is recirculated to the bearing. The tendency is to resort to force feeding of lubricant when shaft rotational speeds exceed several hundred rpm. It is evident that it would be desirable if disk lubrication could be used for speeds substantially greater than 300 rpm to avoid the high cost of a forced lubrication system.
U.S. Pat. No. 3,294,457 describes a self-lubricating bearing that purports to increase the amount of oil that is carried by the disk at higher shaft rotational speeds by having the disk rotate in a semi-circular channel member which has an open top terminating at about the level of the parting line between the upper and lower bearing halves or shells. The lower curved end of the channel is immersed below the oil level in a sump and, although it is not evident that there are openings in the channel for oil to enter, they are likely to be present. The semi-circular channel is concentric with the lower half of the disk. One problem with the arrangement is that one-half of the disk is within the open space of the bearing housing so oil that is centrifuged from the disk at high shaft speeds is not restored to the disk for being scraped off and fed to the bearing. It appears that even though more oil may be held on the disk for part of its revolution, there is little assurance that there will be any more oil on the disk when it reaches the scraper as would be the case if the disk did not rotate through the semi-circular channel.
U.S. Pat. No. 3,777,851, illustrates another disk lubricated bearing in which the problem of oil flow decreasing as disk speed increases is attempted to be solved. In this patented design, the disk and ring that rotates with the shaft has a plurality of cells arranged so as to dip successively into an oil sump and receive charges of oil which are carried to a level above the shaft for gravity discharge into an oil infeed port for the bearing. In this design, the disk is relied upon to provide adequate lubricant when shaft speeds are increased above a certain value.
Several different kinds of scrapers for scraping oil from the periphery of rotating oil transport disk have been tested as reported in a paper presented at the 34th Annual Meeting of the American Society of Lubrication Engineers (1979. The citation is: C.M.Mc.C. Ettles, W. R. Adamson and M. Yiaellouros, "Some characteristics of the Disk-Scraper Oil-Feed Mechanism," Imperial College of Science and Technology, London SW7 2BX, United Kingdom. In the testing apparatus, the authors positioned a straight vertical plate in juxtaposition with and spaced from a vertical line of tangency relative to the lower semi-circular half of the oil transport disk.
Approximately the lower one-half of the plate is immersed in the oil in a sump as is the lower one-half of the disk. The upper half of the plate extends out of the oil in the sump and the top edge of the plate extends up to the level of the horizontal axis of rotation of the shaft. The authors report that the plate gave a slight improvement in the oil transported by the disk.
In accordance with the present invention, the periphery of the oil transport disk rotates between the sidewalls of a shroud whose lower end dips into the oil sump and whose back wall, which bridges the space between the sidewalls, is curved. The curvature is eccentric relative to the disk and the back wall of the shroud converges toward the top of the disk where the oil is scraped from the periphery of the disk. Use of the shroud results in a dramatic increase in the amount of oil carried on the disk's periphery up to the scraper.